Diabetic cardiomyopathy, characterized by myocyte hypertrophy and interstitial fibrosis, is a potentially life-threatening complication resulting from lack of glycemic control. Hypertension associated with diabetes increases disease severity. TGF-beta is the primary effector of fibrosis in response to hyperglycemia. Bioactivation of latent TGF-beta is a major regulatory step in controlling TGF-beta and a logical point for therapeutic intervention. Yet, regulation of TGF-beta bioactivity in these diseases is not well understood. The platelet/matrix protein, thrombospondin l (TSP 1), is a physiologic regulator of latent TGF-beta activation. TSP 1 regulates glucose-stimulated increases in TGF-beta bioactivity and matrix protein synthesis in mesangial cells. TSP-dependent TGF-beta activation is also important for the diabetic myocardium, since high glucose stimulates TSP1 and TGF-beta bioactivity in rat cardiac fibroblasts and increases in TGF-beta bioactivity are blocked with TSP antagonist peptides. Similarly, data show that angiotensin II (Ang 11)-stimulates increased TSP 1 expression and TGF-beta bioactivity that can be blocked by addition of the antagonist peptides. Both glucose and Ang II up-regulate TSP 1 expression, potentially through modulation of PKC and nitric oxide (NO). These data support the hypothesis that glucose-mediated modulation of PKC, NO, ROS, and Ang II are involved in the regulation of TSP1 expression, leading to latent TGF-beta activation, matrix protein synthesis, and myocardial fibrosis. In this proposal, we will use a cultured cardiac fibroblast system to determine 1) the interrelationships between glucose, PKC activity, and oxidative balance in regulation of TSP 1 expression, TGF-beta bioactivity, and matrix protein synthesis and; 2) the role of Ang II in regulation of TSP 1-dependent TGF-beta activation and its relation to glucose stimulation. In addition, rats with diabetes (streptozotocin) and hypertensive diabetes will be used to determine 3) whether peptide antagonists of TSP-mediated TGF-beta activation ameliorate diabetic myocardial fibrosis under normo- and hypertensive conditions. These studies will further our understanding of how TGF-beta is regulated in diabetes and hypertension, and will potentially identify new strategies for therapeutically attenuating myocardial fibrosis.